Foam materials are currently used as sealing materials in various fields such as architecture, civil engineering, electrics, electronics, and vehicles. Examples of the foam materials used as sealing materials include thermoplastic resin foams comprising resins such as polyethylene resin and polypropylene resin, and rubber foams comprising rubbers such as synthetic rubbers and natural rubbers.
Of the sealing materials, water-resistant sealing materials are used for filling gaps of various structures such as buildings, electric devices, and vehicles to prevent water infiltration into the structures. The water-resistant sealing material is placed at a place to be sealed in its compressed state, and resilient stress generated by shape recovery from its compressed state allows the sealing material to closely adhere to the interface of the sealed place without a gap.
In the case where the water-resistant sealing material has low flexibility against compression, the water-resistant sealing material generates too high resilient stress, resulting in deformation of the sealed place. The deformation of the sealed place causes expansion of the gap of the structure. This results in decrease in adherence (hereinafter, referred to as sealability) of the water-resistant sealing material to the sealed place, thereby causing insufficient water resistance.
Accordingly, open-cell foam materials are used as the water-resistant sealing materials as the open-cell foam materials have excellent flexibility against compression. On the other hand, the open-cell foam material contains cells communicating with one another. This causes easy infiltration of water into the foam material, resulting in poor water resistance. In the case where the open-cell foam material absorbs water to swell and thereby achieves good sealability, the open-cell foam material has poor sealability until it sufficiently absorbs water, and thus, the open-cell foam material allows water to infiltrate therein before achieving sufficient sealability.
A foam material containing both closed cells and open cells is also used as the water-resistant sealing material. In such a foam material, the closed cells contribute to good water resistance, and the open cells contribute to good flexibility against compression. For example, Patent Document 1 discloses a foam material which contains both closed cells and open cells. In that foam material, eight or more cells per 1 cm in length are contained.
Disadvantageously, the resilient stress generated by the regular sealing material is reduced when the water-resistant sealing material is used for a long time. This causes reduction in sealability, resulting in insufficient water resistance.
Patent Document 1: Japanese Kokai Publication H09-111899 (JP-A H09-111899)